The rise of warmer air and the sinking of colder air creates significant variation in air temperatures between the ceiling and floor of buildings with conventional heating, ventilation and air conditioning systems. Such air temperature stratification is particularly problematic in large spaces with high ceilings such as warehouses, gymnasiums, offices, auditoriums, hangers, commercial buildings, and even residences with cathedral ceilings, and can significantly decrease heating and air conditioning costs. Further, both low and high ceiling rooms can have stagnant or dead air. For standard ceiling heights with duct outlets in the ceiling there is a sharp rise in ceiling temperatures when the heat comes on.
One proposed solution to air temperature stratification is a ceiling fan. Ceiling fans are relatively large rotary fans, with a plurality of blades, mounted near the ceiling. The blades of a ceiling fan have a flat or airfoil shape. The blades have a lift component that pushes air upwards or downwards, depending on the direction of rotation, and a drag component that pushes the air tangentially. The drag component causes tangential or centrifugal flow so that the air being pushed diverges or spreads out. Conventional ceiling fans are generally ineffective as an air de-stratification device in relatively high ceiling rooms because the air pushed by conventional ceiling fans is not maintained in a columnar pattern from the ceiling to the floor, and often disperses or diffuses well above the floor.
Another proposed solution to air temperature stratification is a fan connected to a vertical tube that extends substantially from the ceiling to the floor. The fan may be mounted near the ceiling, near the floor or in between. This type of device may push cooler air up from the floor to the ceiling or warmer air down from the ceiling to the floor. Such devices, when located away from the walls in an open space in a building, interfere with floorspace use and are not aesthetically pleasing. When confined to locations only along the walls of an open space, such devices may not effectively circulate air near the center of the open space. Examples of fans connected to vertical tubes are disclosed in U.S. Pat. No. 3,827,342 to Hughes, and U.S. Pat. No. 3,973,479 to Whiteley.
A device that provides a column of air that has little or no diffusion from the ceiling the floor, without a vertical tube, can effectively provide air de-stratification. U.S. Pat. Nos. 4,473,000 and 4,662,912 to Perkins disclose a device having a housing, with a rotating impeller having blades in the top of the housing and a plurality of interspersed small and large, vertically extending, radial stationary vanes spaced below the impeller in the housing. The device disclosed by Perkins is intended to direct the air in a more clearly defined pattern and reduce dispersion. Perkins, however, does not disclose the importance of a specific, relatively small gap between the impeller blades and the stationary vanes, and the device illustrated creates a vortex and turbulence due to a large gap and centrifugal air flow bouncing off the inner walls of the housing between the blades and vanes. Perkins also discloses a tapering vane section. The tapering vane section increases velocity of the exiting air stream.
A device with a rotary fan that minimizes the rotary component of the air flow while maximizing the axial air flow quantity and velocity can provide a column of air that flows from a high ceiling to a floor in a columnar pattern with minimal lateral dispersion that does not require a physical transporting tube. Such a device should reduce the energy loss by minimizing the rotary component of the air flow, and therefore minimizes turbulence. Such a device should minimize back pressure, since a pressure drop at the outlet of the device will cause expansion, velocity loss and lateral dispersion. The device should have minimum noise and low electric power requirements.